Appendix D Experience+ in the United Kingdom on the Control of Discharges of Sewage Sludge to Estuarine and Coastal Waters, A Case Study INTRODUCTION In the text of this book, the physical, chemical and biological processes which take place in estuaries and coastal waters have been described in detail so far as current knowledge allows. General descriptions have also been provided on how our understanding of these processes may be used to predict the environmental impact of waste disposal on the marine environment and the assimilative capacity of the receiving waters. The conclusion has been reached that the ocean does have a capacity to receive certain wastes without damage, but that it is essential that this assimilative capacity be quantified and managed effectively through adequate controls, in order to ensure that disposal does nat give rise to adverse effects on the receiving waters, the biota present or humans as the consumer of marine resources. Due largely to its extensive coastline and the proximity of much of its population to estuaries or coastal waters, the United Kingdom UK! has a long history of discharging sewage effluent after varying degrees of treatment! directly ta estuaries and coastal waters. In addition, approximately 28 percent of the sewage sludges produced by the treatment of sewage within the UK is disposed of at sea by dumping from vessels. These dispasal practices are controlled under national and, in some cases, international regulations. Dumping of wastes at sea is regulated by the Dumping at Sea DAS! ACt 1974, and by the provisions of the Oslo and London Conventions on the prevention of marine pollution. Discharge to estuaries and coastal waters is regulated under the Rivers Prevention of Pollution! Acts of 195l and 1961 and by the Control of Pollution Act 1974, which, when fully implemented, will extend controls to all discharges ta estuarine and coastal waters. The Paris Convention on 950 the Prevention of Marine Pollution f rom Land-based Sources provides an international framework for these national controls on discharges to coastal waters. All these regulations both national and international! place their emphasis on the prevention of pollution from the disposal of waste and not the prevention of disoharees per se. Pollution is defined in slightly different ways in the respective laws and regulations, but all are generally consistent with the definition given by GESAMP The UN's Group of Experts on the Scientific Aspects of Marine Pollution.!: "Pollution is the introduction by man, directly or indirectly, of substances or energy into the marine environment including estuaries! resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to marine activities including fishing, impairing of quality of use of seawater and reduction of amenity." In regulating the discharge of wastes to estuaries and coastal waters to avoid pollution, UK authorities* have carried out assessments of the environmental impact of disposal practices for some years which have necessitated the application of the techniques and knowledge set out in this book. The presentation of detailed case histories for some of the most important areas off the UK is intended to assist in the interpretation and application of these predictive and monitoring techniques. In particular, the use of pre-discharge studies of the waste and the characteristics of the receiving area to predict the dispersion pathways, the ultimate fate of the waste and its constituents, together with its effects on biota will be described. The results of monitoring after commencement of discharge to confirm the validity of the predictions made and to measure biological, chemical and physical effects in the water column and at the seabed will also be presented. * Regulatory Authorities are: Dumping at Sea Act, 1974; Ministry of Agriculture, Fisheries and Food RAFF! for England, Department of Agriculture and Fisheries for Scotland, Secretary of State for Wales and the Department of the Environment for Northern Ireland. Control of Pollution Act, 1974: Regional Water Authorities in England and Wales and River Purification Boards in Scotland. 951 The three areas selected as examples in this case study are those where the largest quantities of sewage sludge are dumped the Outer Thames Estuary and Liverpool Bay for England, and the Firth of Clyde for Scotland! . Although the emphasis will be on the application of scientific techniques to regulate dumping, reference will also be made to the control of sewage discharges to the Thames Estuary and to the importance of dumping relative to other pollutant inputs in all three areas. THE THPd4KS ESTUARY Sewa e Slud e Dum in used for the dumping of sewage sludge from London since 1887. Prior to 1967 the sewage sludge was deposited in the Black Deep, shown in Figure D.l, which had also been used for the deposit of dredged spoil up to 1964. Since 1967, the sewage sludge has been dumped in the adjacent Barrow Deep; no other wastes have been dumped at this location Figure D.l! . The sewage sludge ar ises a t two large sewage treatment plants operated by the ThamesWater Authority and located in eastern London-Beckton { serving a population of 3.13 million! and Crossness serving a population of 1.6 mi11ion! which provide primary and secondary biological activated sludge! treatment for 60 percent of London's sewageflow. Approximately 90 percent of the sludge is digested in heated anaerobic digesters to reduce the quantity of sludge, control odour, and generate gas for po~er generation on site! before loading into dumping vessels of 2,000 to 2,600 metric ton tonne! capacity for transportation to the dumping area 74 km downstream. The composition and quantity of sludge dumped each year has varied slightly. Since statutory control under the DAS Act started in 1974, the most noticeable change has been a reduction in the concentration of mercury through tighter controls on industrial discharges to the sewage works by the Thames Water Authority. The quantity of sludge dumped, its average composition, and the total mass loads of its constituents are presented in Table D.l for 1974 to 1977. 952 Figure D. l The Outer Thames Estuary 953 Ot Cl lo ICI Co O Ch O ~ h ~ h Ch CO C4 4C 0 r CO OCO hr ot In r Ol C r + + '4I Ih In O O O O r rt r r 0 IO In I I IO Cl O ~ h Pl R Cl JkIO OC lh O Ol e + w r o r gl C IO Co CO Ih C0 C Ih OC W Ch SC IO4J IO5 rIrl C 0 IO Ctr O O CC O O O O t A nl O r H cC nt JJ Cr or o INI cn 8 0 V O IO OCIO O IC ~ h lh Ctl CV H IO hr r Cl Ot Ch ~ ~ Or Co 8 8 co ICC C C0 C Ih co 4 r cn Ih C Irt C + + 0 ID Irt O co O O O O I + CC CO H 92 H nl ctr ln IO O ro 0 V CO a m w co 4I ln O ht O CO CO W CO Ct lcl Ict w ol Cct or CO CO C3, 0 ht CO CS C 4 0 4 IO 0 + + V ol lo O H C r Ct W 4 Ot 0 O CO 0 O O O I cC CC OI8 O lh Ih IO ht OC O In IOCÃl CJ Ih CO r ~ 0 CS cn C 4 Ilr 4 8 8 84 0 40IS 40 40 V W I4 ~ I 4 IS Ot AJIS SC0 O '0 4 M IO Otlo '0Ch 40 C 8 C d g 5 C 0 IO 0 Ilrl 4 lit IO M Crl 4 R, IS IO 4 Ct0 a 0 0 4 K~ o CP 40 4 C Ch 4 C 0 4 4 4 4 OCC C IO OI V X V CO K Ol V + ~ 954 Estimates have been made of the relative inputs of organics, nutrients and trace metals to the outer estuary from dumping, discharges of effluent, river discharges and atmospheric deposition see Table D.2! . Even from the point of view of the whole outer estuary, it is seen that sludge dumping is a very significant input for several constituents and, within the immediate vicinity of the dumping area which is relatively remote from other point source discharges, dumping is clearly the dominant anthropogenic source of the substances listed. Table 0.2 Sstimate of Relative Inputs to the Outer Thames Estuary, 1977 National Water Council, 1979! . Percent of Total Contribution Suspended Total Total Source Solids BOD 8 P Cd Cr Cu Hi Pb 'Zn 8 River Inputs 40 12 47 22 69 35 34 43 20 35 33 Sewage s Industria1 Discharge 30 46 43 66 16 26 19 34 1.8 22 Dumping 30 42 9 12 12 36 42 21 54 40 67 Atmospheric Deposition 3 1 5 2 6 3 KK'RKKRKKRKRRRK KRRKKRXKD'RIZRR KC 5i RZ CR KR The use of the outer estuary for waste disposal must be compatible with a number of other activities in the region. These include navigation for vessels discharging or loading in the Port of Kondon, extraction of sand and gravel from licensed areas to the northeast of the dumping ground, and commercial exploitation of fish and shellfish stocks value in 1978 of about one million pounds per annum! . The area is of limited amenity use offshore, but, important bathing beaches are located at Southend and from Walton northwards Figure D.l!. This section will present the results of work carried out by Ministry of Agriculture, Fisheries and Pood MAFF! from 1972 to 1978 to determine the initial dispersion paths of the sludge, subsequent transport processes in the water column and sediments, the effects of disposal on the physical and chemical 955 characteristics of the receiving area and effects on the biota.